W206 Pickleworm Frank A. Hale, Professor; Carla Dilling, Graduate Research Assistant; and Jerome F. Grant, Professor, Entomology and Plant Pathology The pickleworm, Diaphania nitidalis (Stoll) (Fam- Figure 1. Pickleworm larvae, adult, pupa and egg (enlarged) ily Crambidae, previously Pyralidae), is found from (Images courtesy of North Carolina Cooperative Extension Service). Canada into parts of South America, and as far west as Oklahoma and Nebraska. It is an important pest of numerous cucurbits. Summer squash is the preferred host, but it also feeds on cantaloupe, cucumber, pump- kin and winter squash. Late-planted cantaloupes are heavily attacked in some areas. Damage The destructive stage of this insect is the larval stage. Larvae feed on, and tunnel into, the flowers, vines and fruits. Young larvae usually feed on internal portions of blossoms, leaf buds or growing tips of vines. Older larvae, on the other hand, will bore into the fruit of the plant, depositing excrement (frass) as they feed and move throughout the fruit. Damaged fruit usually sours, spoils and rots. Vine damage occurs when larvae bore into the vine, preventing its growth and causing its ultimate death. Numerous feeding holes may be found along the vines. In the Southeastern United States, damage from pickleworms is not usually seen until late August or early September. Description and Life Cycle Adults are small moths with a wingspan of about 1¼ inches and a large, light-colored to yellow spot near the center of each dark-colored forewing. The tip of the abdomen contains a cluster of brush-like hairs. The small, white to pale-colored eggs are laid singly or in small clusters directly on the foliage. Pickleworms undergo five larval instars; all larvae have three pairs of legs near the head and five pairs of fleshy prolegs. Newly hatched larvae are colorless; as the larvae get older, they undergo several different colorations and patterns. The younger larvae have a row of small dark tubercles, each with a dark seta (hair) on each segment. The more mature larvae, which are light yellow to green, lose the dark coloration of the tubercles. Larvae usually form a silken cocoon on the foliage, where they pupate. Pupae are brown and about 0.6 inch long. Figure 2. Adult and larva of the pickleworm (Photographs courtesy of J. L. Capinera, University of Florida). Adult Larva The pickleworm does not overwinter in our area. Established biological control organisms, such as It overwinters in semi-tropical areas, like the southern- predators, reduce populations of pickleworms but can- most areas of Florida and Texas, migrating northward not be depended upon to prevent infestations. Effec- in the spring. The time between egg and adult emer- tive scouting for pest and biological control organism gence is 17-20 days. Eggs are deposited on cucurbit populations can help you determine their effectiveness surfaces during midsummer. In approximately three in your cropping system. Unfortunately, no effective days, pickleworm larvae hatch and begin to feed; about commercial biological controls for pickleworm are two weeks later, the larvae begin to roll leaves together readily available at this time. The use of the nematode where they will pupate inside the rolled leaves or within Steinernema carpocapsae Weiser is promising, as it has the silken cocoon attached to the foliage or plant debris been shown to suppress pickleworm injury in squash. on the ground. Adult moths will emerge about one week Research also is underway to evaluate a variety of gen- later. There are usually two or three generations per eralist predators against pickleworm, such as Calosoma year, depending upon temperature and environmental spp. and Harpalus spp. conditions. Chemical Controls Control Applications of a registered and approved insecti- Non-chemical Controls cide should begin immediately when pickleworm larvae Several non-traditional methods are available to are first found in blossoms or buds or when their dam- help to reduce populations of pickleworms. These in- age first appears. Pickleworms must be killed before clude the use of resistant varieties, cultural control, they enter the fruit. Several chemical insecticides give mechanical control and biological control. Planting va- good control, but timing is critical. When applying an rieties of cucurbits resistant to pickleworms is effective insecticide to a specific crop, always follow the pre- for those plants where resistant varieties are available. harvest interval (PHI) on the insecticide label. The PHI For example, experiments in North Carolina have shown states when the last insecticide application can be made distinct differences in the susceptibility or resistance of prior to harvest. Commercial vegetable growers have squash varieties to pickleworms. (More resistant variet- access to more chemical control options. If possible, it ies are Butternut 23, Summer Crookneck, Early Pro- is best to apply chemical insecticides in early evening lific Straightneck and Early Yellow Summer Crookneck; when blossoms are closed to minimize toxic effects to more susceptible varieties are Cozini, Black Zucchini bees. Caserta, Zucchini, Shrot Cofozella and Benning Green Tint Scallop.) The availability of chemical pesticides changes regu- larly. Always consult your local county Extension agent for Cultural controls include planting the crop early a list of currently approved and recommended chemical − this early-planting enables growers to harvest most insecticides. The following links provide access to listings of the crop before the pickleworm can cause excessive of recommended chemical control options for homeown- losses. Early plantings are seldom damaged, depending ers and commercial production growers: upon the arrival of the pickleworm into Tennessee from southern areas. Some mechanical controls also have • “UT Extension Insect and Plant Disease Control been shown to be effective. For example, susceptible Manual” (vegetables, home garden insects): plants can be covered with screened material (floating http://eppserver.ag.utk.edu/redbook/pdf/ho row covers) to prevent adult moths from laying eggs on megardeninsects.pdf the plants. However, this method can add expenses to the production budget due to purchase of additional • “Southeastern U.S. Vegetable Crop Handbook” materials. To reduce numbers of subsequent genera- (commercial growers): tions in a given season, growers can destroy infested http://www.sripmc.org/docs/SoutheasternVeg vines and unused or rotting fruits as soon as the crop is etableGuide.pdf harvested. Stems infested with pickleworms can be slit and the borers removed. Soil can then be placed over Always use pesticides according to the label; also the injured stem to encourage rooting. use protective clothing and dispose of remaining pesti- cide in a properly approved manner. References (and Internet Sites) North Carolina State University, Insect and Related Pests of Vegetable Crops (edited by K. A. Sorensen and J. R. Baker): http://ipm.ncsu.edu/AG295/html/index.html http://www.ces.ncsu.edu/depts/ent/notes/Vegetables/veg001e/veg001e.htm University of Florida: http://creatures.ifas.ufl.edu/veg/pickleworm.htm Visit the UT Extension Web site at http://www.utextension.utk.edu/ W206-4/09 09-0136 Programs in agriculture and natural resources, 4-H youth development, family and consumer sciences, and resource development. University of Tennessee Institute of Agriculture, U.S. Department of Agriculture and county governments cooperating. UT Extension provides equal opportunities in programs and employment..